1. Field of the Invention
The present invention relates to a speaker unit of a composite coaxial type suitable for use as a speaker unit installed in a car, for example.
2. Description of the Related Art.
In the prior art, when a plurality of speakers handling different frequency bands are disposed in a narrow space, the speakers are made as a composite coaxial type of, for example, a two-way system. By arranging the composite coaxial type speaker, as compared with a case where speakers for middle or intermediate frequency sound and low frequency sound are located at different positions in a single cabinet, a sound of intermediate frequency band together with a sound of low frequency band, of course, is emitted from substantially the center position of a speaker for low frequency sound so that the directivity such as a sound image localization or the like is improved.
Further, such a woofer or low frequency sound speaker in which an opening of a cone type diaphragm on its sound emitting side is shaped as an ellipse is used widely. By making the sound emitting opening of the diaphragm as an elliptic shape, it is advantageous when the speaker unit is installed in a limited narrow space such as in a car or the like.
Under the concept mentioned above, in a low frequency sound speaker, or an ellipse type speaker in which a front end, namely a sound emitting opening portion of a cone type diaphragm is made of an ellipse, there is proposed an intermediate or middle frequency sound speaker which is disposed in such a manner that the sound emitting opening portion of the cone shape diaphragm is concentric at the center position of the diaphragm at the front portion of the diaphragm of the low frequency sound speaker.
In case of such a composite coaxial type speaker, there are generated much cross modulation distortions near the cross-over frequency of each of the low and intermediate frequency band speakers and many crests and troughs are caused on a frequency characteristic curve. Hence, it is difficult to obtain a flat characteristic, which lowers the sound quality.
The fact that the sound emitting opening of the low frequency sound speaker is of an ellipse means that the ellipse has a long diameter direction and a short diameter direction.
Since there is coaxially located the intermediate frequency sound speaker, the sound emitting opening of which is of circle, the sound wave emitted forward from the long diameter direction and the sound wave emitted forward from the short diameter direction are reflected on and differected by the rear portion of the circular intermediate frequency sound speaker, namely its frame. As a result, there is caused a phase difference between the sound wave emitted from the long diameter direction and the sound wave emitted from the short diameter direction. This phase difference becomes the distortion which deteriorates the frequency characteristics. Further, the directivities of the sound waves emitted from the long and short diameter directions are different each other and hence the directivity characteristic is deteriorated.
An object of the present invention is to provide a speaker unit which solves the problems mentioned above.
According to an aspect of the present invention, there is proposed a coaxial type speaker, in which a low frequency sound speaker, the sound emitting opening of a diaphragm of which is of an ellipse and at least an intermediate frequency sound speaker, the sound emitting opening of a diaphragm of which is of an ellipse, are arranged coaxially, whereby the difference between directivity characteristics of the sound waves in the long diameter direction and the short diameter direction of the elliptic type low frequency sound speaker is removed and hence the frequency characteristics are improved.
According to another aspect of the present invention, there is provided a composite coaxial speaker unit in which an elliptic type intermediate and high frequency sound speaker is disposed on the center axis of an ellptic type low frequency sound speaker at its front sound emitting opening portion, and the sound emitting opening portion of a diaphragm of the elliptic type low frequency sound speaker and the sound emitting opening portion of a diaphragm of the elliptic type intermediate and high frequency sound speaker are made as a similar figure substantially.
According to the speaker unit of the present invention, since the intermediate and high frequency sound speaker arranged coaxial with the center of the elliptic type low frequency sound speaker is made as an ellipse similar to the low frequency sound speaker, a speaker unit, the frequency characteristics and the directivity characteristics of which are improved and which is suitable to be installed on a car, can be obtained.